1. Field of the Invention
The present invention relates to a system and method for treating biological vessels and, more particularly, to an angioplasty balloon catheter having an expandable constraining structure positioned over the balloon and configured for constraining balloon inflation thereby enabling isolated balloon regions to protrude from the constraining structure during inflation.
2. Description of the Related Art
Percutaneous transluminal angioplasty (PTA) is a procedure in which a balloon catheter is inserted through an artery and guided to the region of lumen narrowing. The balloon is inflated to force the plaque material (typically fat and calcium) against the wall of the artery to open the vessel lumen and improve blood flow.
Angioplasty balloons are typically cylindrical when inflated and have different lengths and diameters to conform to different vessel sizes. The balloons are inflated at high pressure, normally between 8-20 atmospheres, in order to overcome the resistance of the plaque and achieve luminal expansion.
High pressure angioplasty is often traumatic to the vessel walls and can lead to vessel wall dissections. Such dissections are common and can be severe and may require urgent surgery or placement of stents. In addition, dissection may contribute to poor long term clinical results and restenosis even if a stent is placed in the treated lesion.
Dissections are usually attributed to several mechanisms occurring during balloon inflation including shear forces applied on the vessel walls as the balloon pleats unfold as well as uneven balloon inflation which occurs as a result of the non-symmetric nature of the vascular disease.
Shear forces result from balloon unfolding and an increase in balloon diameter in the radial direction as the folded balloon unwraps. As the folded pleats of the balloon open, the layers slide over one another and apply tangential forces to the lesion and/or vessel wall which can abrade the lesion or vascular wall and in the worst instances cause dissections.
Uneven inflation results from the uneven nature of the disease in the vessel. Angioplasty balloons are commonly non-compliant or semi-compliant, and when semi-compliant balloons are inflated against an eccentric lesion, the balloon will follow the “path of least resistance” and its diameter will increase more in the less diseased sections of the vessel (causing a dog bone effect), often increasing trauma in these areas.
Due to the above limitations, standard balloon catheters are also incapable of applying local forces sufficient to open to resistant plaque regions and thus can be ineffective in providing ample patency in highly calcified lesions, such as those prevalent in peripheral arteries.
Attempts to solve the above limitations of balloon catheters by increasing local forces via cutting or scoring elements (blades/wires) positioned on the balloon surface (e.g. US20040143287 and US20060085025) were somewhat successful at opening resistant lesions but did not adequately solve the aforementioned problems resulting from balloon unfolding and uneven inflation.
Thus it would be highly advantageous to have an angioplasty balloon catheter configured for minimizing trauma and dissection to the blood vessel walls as the balloon is inflated as well as for enabling application of local forces to discrete lesion regions that are resistant to opening.